Add wheel event supportfor htmlbackend

Author: alt-tosc

src/fidget/dom2.nim

@@ -1154,6 +1154,13 @@ type
     screenX*, screenY*: int
     x*, y*: int
 
+  WheelEvent* = ref WheelEventObj ## see `docs<https://developer.mozilla.org/en-US/docs/Web/API/WheelEvent>`
+  WheelEventObj {.importc.} = object of MouseEvent
+    deltaX*: float64
+    deltaY*: float64
+    deltaZ*: float64
+    deltaMode*: uint32
+
   DataTransferItemKind* {.pure.} = enum
     File = "file",
     String = "string"

src/fidget/htmlbackend.nim

@@ -519,6 +519,12 @@ proc startFidget*(draw: proc(), load: proc() = nil, w = 0, h = 0) =
     ## Scroll does not need to do anything special in HTML mode
     refresh()
 
+  dom.window.addEventListener "wheel", proc(event: Event) =
+    ## When wheel is used
+    let event = cast[WheelEvent](event)
+    mouse.wheelDelta += vec2(event.deltaX, event.deltaY)
+    refresh()
+
   dom.window.addEventListener "mousedown", proc(event: Event) =
     ## When mouse button is pressed
     let event = cast[MouseEvent](event)